Method of transporting mineral oils



3 b'tAHUH R! 1967 J. G. SAVINS ETAL 3,295,542

METHOD OF TRANSPORTING MINERAL OILS Filed June 29, 1964 (D O l 8INVENTORS DAVID B. COX

JOSEPH G. SAVI NS BY M fi ATTORNEY United States Patent 3,295,542 METHODOF TRANSPORTING MINERAL OILS Joseph G. Savins, Dallas, Tex., and DavidB. Cox, Sewell,

N.J., assignors to Mobil Oil Corporation, a corporation of New YorkFiled June 29, 1964, Ser. No. 378,580 9 Claims. (Cl. 137-13) Thisinvention relates to the transportation of mineral oils and moreparticularly to the pipeline transportation of mineral oils attemperatures at or near their pour points.

The transportation through pipelines of highly viscous mineral oils suchas petroleum crude oils and shale oils in relatively cold weather hasheretofore presented great difficulties. Many naturally occurring crudeoils and shale oils become semisolids at low temperatures due to thepresence of solid particles of wax, asphaltenes or resins which growtogether at points of contact to form a structural matrix. This propertyof these oils is characterized by the ASTM (American Society for TestingMaterials) pour point which is that temperature below which the oil willnot pour from a standard container under certain specified conditions.See W. L. Nelson, Petroleum Refinery Engineering, McGraw-Hill Book 00.,1110., Fourth Edition 1958, pages 26 and 27.

The pour point has been accepted by pipeline engineers as thecontrolling factor of pipeline flow. Thus, where the normal temperatureof a mineral oil is less than its pour point, it has been the practiceto depress the pour point below the normal temperature by the use ofadditives such as light hydrocarbons or to heat the oil to a temperatureabove its pour point prior to pipelining. In fact, even in those caseswhere a mineral oil is normally a few deg-recs above its pour point ithas been customary in pipeline operations to heat the oil or to diluteit by adding light hydrocarbons. Both of these practices are expensiveand inconvenient. The former practice requires the installation ofheating equipment at intervals along the pipeline and, in addition,steps must be taken to insulate the pipeline against heat loss. Thelatter practice may require that the diluent fluid be separated from thecrude oil at the terminal point. In addition, the use of a diluent ispractical only in those localities where a sufiicient supply of lighthydrocarbons is available.

It is an object of this invention to overcome the difficulties involvedin the transportation by pipeline of relatively viscous mineral oils andto provide a method whereby such oils may be transported without the useof additives or the unnecessary use of heating equipment.

This invention is based upon the discovery that a mineral oil exhibitingpour point characteristics may be transported through a pipeline at atemperature below or at the pour point at rates which approach, and insome cases even exceed, the rates possible when the oil is above itspour point. Thus, in carrying out the invention, a mineral oil istransported through a pipeline extending from a shipping point to aterminal point at a temperature near its pour point and under certainconditions of flow rate and pipeline diameter. In a further aspect ofthe invention, an oil which normally is at a temperature above or belowits pour point is brought to a temperature near the pour point beforepumping it through the pipeline un der the aforesaid conditions.

For a better understanding of the invention, reference may be had to thefollowing detailed description and to the drawing which shows a seriesof curves illustrating the advantages which may be obtained by thepipeline transportation of a mineral oil at or near its pour point.

In order to illustrate the invention, reference is made to the resultsof tests carried out on a shale oil in order to determine its flowcharacteristics at varying tempera- 3 ,295,542 Patented Jan. 3, 1967"ice tures in a pipeline. The physical properties of this shale oil areset forth below in Table I.

TABLE I Specific Gravity at F .9377 ASTM Distillation:

Initial Boiling Point F 24-4 48% Cracked F 664 ASTM Pour Point F 80Viscosity:

130F SUS* 93.9

210 F. SUS*.. 43.8 Density:

*Saybolt universal seconds.

From the tests it was possible to determine the pressure gradients inpounds per square inch (p.s.i) per thou sand feet of horizontal pipelinenecessary to move the shale oil through the pipeline at differenttemperatures and flow rates. These pressure gradients in p.s.i perthousand feet for 15%, 12%" and 10% I.D. pipes are set forth in TablesII, III, and IV, respectively. The flow rates are given in units of 1000barrels per day wherein 1 barrel equals 42 US. gallons.

TABLE II15% I.D. PIPE Flow Rate (1,000 Bbls. per Day) Temp,

TAB LE III12% I.D. PIPE Flow Rate (1,000 Bbls. per Day) Temp, F.

TABLE IV -10% I.D. PIPE Flow Rate (1,000 Bbls. per Day) Temp., F.

The data set forth in Tables II, III, and IV show, surprisingly enough,that heating the shale oil above the pour point does not appreciablyenhance the pumpability of the oil at the rates likely to be encounteredin pipeline operations. More particularly, the data set forth in TableII shows that at rates of from 65,000 to 100,000 barrels per day for the15%" pipe, the pressure drop at the pour point (80 F.) is for the mostpart as low as, and in many cases lower than, the pressure drop at 90 F.or even at 100 F. For example, at a flow rate of 72,000 barrels per day(Table II), the pressure drop at the pour point is .21 p.s.i. perthousand feet of line; whereas the pressure drop is .22 p.s.i. at atemperature of 90 F. or a temperature of 100 F.

In some instances, a slight decrease in pressure gradient can beobtained by heating the oil to a temperature above the pour point. Forexample, at a flow rate of 100,000 barrels per day through the 15%"pipe, the pressure gradients per thousand feet at 90 F. and 100 F. are.40 p.s.i. and .37 p.s.i., respectively, as compared with a pressuregradient of .42 p.s.i. per thousand feet at the pour point. However, thedecreases are so small, e.g., less than 5 percent due to heating the oilfrom 80 F. to 90 F., that the benefits obtained due to the reducedpumping requirements would in most cases be offset by the expenseinvolved in installing and operating the necessary heating system.

From an examination of the above-noted and other data set forth inTables II, III, and 1V, it is apparent that little or no economicbenefit can be gained :by heating the oil to a temperature above itspour point. In fact, it is advantageous under certain conditions to coolan oil which is normally at a temperature above its pour point down tothe pour point. For example, for the 15% pipe, cooling the oil from 90F. to 80 P. will result in a 30 percent decrease in the pressuregradient for a flow rate of 90,000 barrels per day.

A portion of the data set forth in Table II is illustrated in thedrawing where the oil temperature (T) in degrees Fahrenheit is plottedagainst the log of the pressure gradient (AP) in pounds per square inchper thousand feet. With reference to the drawing, curves 1-7 show therelationship between pressure drop and temperature in the range of 50 F.to 100 F. for flow rates of 65,000, 72,000, 80,000, 90,000, 95,000,98,000, and 100,000 barrels per day, respectively. As shown in thedrawing, at flow rates within the range of 72,000 barrels per day (curve2) to 98,000 barrels per day (curve 6), the pressure drop at the pourpoint is less than the pressure drop at the temperature 10 F. above thepour point, i.e., 90 F. Similar ranges also exist for the 12%" pipe(Table III) where the limits are 48,000 and 65,000 barrels per day andthe 10%" pipe (Table IV) where the limits are 34,000 and 44,000 barrelsper day. These ranges expressed in terms of the ratio of flow rate inthousands of barrels per day (Q) to the square of the pipe diameter ininches (D are .31-.42, .32-.43, and .32-.42 for the 15%", 12%", and 10%"pipes, respectively. From this it can be seen that where the ratio Q/Dis within the range of .32.42, a reduction in pressure gradient can beachieved by cooling the oil to the pour point. Cnversely, where the oilnormally is at or below the pour point, no advantage results fromheating the oil to a temperature above the pour point when the ratio Q/Dis in the range of .32-.42.

The test results described above show that under the specifiedconditions of flow rate and pipe diameter, optimum results are obtainedby flowing the oil through the pipeline at its exact pour point.However, it will be recognized that some latitude must be allowed inactual operations due to the difficulties involved in rigidlycontrolling the temperature of the oil. Moreover, at temperatures in thevicinity of the pour point, the change in pressure gradient withtemperature is much less than at some temperatures further from the pourpoint. For example, in all of the cases represented by curves 1-7 of thedrawing, the pressure gradient decreases with increasing temperature upto the pour point with the greatest relative reduction occurring betweenabout 60 F. to 75 F. Within F. of the pour point, the date of pressuregradient reduction with increasing temperature is much less 4 than thatwithin the aforementioned range. Therefore, in accordance with theinvention, the oil is transported through the pipeline at a temperaturewithin at least 5 F. of its pour point and preferably at the pour pointor as near thereto as practical.

In the application of the invention to the pipeline transportation of amineral oil, the oil is transferred to a pipeline which extends from ashipping point, e.g., a storage facility or a processing installationsuch as a shale-oil extraction plant, to a suitable terminal point. Afirst pumping station may be located adjacent the shipping point and, ifnecessary, additional pumping stations may be located at intervals alongthe pipeline in a manner well known to those skilled in the art. The oilis flowed from the shipping point through the pipeline to the firstpumping station and then pumped through the pipeline at a temperaturewithin 5 F. of its pour point and at a flow rate such that the ratio Q/Dis within .32.42.

If the oil has a pour point sufficiently near its basic temperature,i.e., the normal temperature of the oil at the shipping point, the oilcan be pipelined without the use of heating or cooling equipment.However, in those cases where the basic temperature of the oil issignificantly above or below the pour point, the temperature of the oilis adjusted to a temperature within 5 F. of the pour point andpreferably to the pour point. Thus, in the application of the inventionto a mineral oil having a basic temperature lower, particularly by morethan 5 F., than its pour point the oil is heated to within 5 F. of thepour point in order to gain a reduction in pressure drop through thepipeline. Preferably, the oil is not heated above the pour point, sinceno further pressure gradient reduction results where the ratio Q/D iswithin the range of 32-.42. In this embodiment of the invention, thepipeline may be insulated or heating stations may be installed atintervals along the pipeline in order to maintain the oil at atemperature within 5 F. of its pour point.

As noted above, a further aspect of the invention involves the pipelinetransportation of a mineral oil having a pour point less than its basictemperature. In this case, the oil is cooled to within 5 F. of its pourpoint, and preferably to a temperature not less than the pour point, andpumped through the pipeline at a flow rate such that the ratio Q/D iswithin the range of .32-.42. If necessary in maintaining the oil at ornear its pour point, the oil may be passed through cooling stationslocated at intervals along the pipeline. Also, the pipeline may besuitably insulated in the event the ambient temperature is significantylhigher than the pour point of the oil.

Having described specific embodiments of the invention, it is understoodthat further modifications may become apparent to those skilled in theart and it is intended to cover all such modifications as fall withinthe scope of the appended claims.

We claim:

I. In a method of transporting a mineral oil, the steps of flowing saidmineral oil through a pipeline extending from a shipping point to aterminal point at a temperature within 5 F. of its pour point in atleast a portion of said pipeline, and maintaining the flow rate of saidoil such that the ratio of said flow rate in thousands of barrels perday to the square of the inner diameter in inches of said pipeline isnot less than .32 nor more than .42 for said portion of said pipeline.

2. The method of claim 1 wherein said mineral oil is at its pour pointin said portion of said pipeline.

3 In a method of transporting a mineral oil having a pour pointdifferent from its basic temperature, the steps of adjusting thetemperature of said mineral oil in the direction of its pour point to atemperature within 5 F. of its pour point, flowing said mineral oilthrough a pipeline extending from a shipping point to a terminal pointat a temperature within 5 F. of its pour point in at least a portion ofsaid pipeline, and maintaining the flow rate of said oil such that theratio of said flow rate in thousands of barrels per day to the square ofthe inner diameter in inches of said pipeline is not less than .32 normore than .42 for said portion of said pipeline.

4. In a method of transporting a mineral oil having a pour point lessthan its basic temperature, the steps of cooling said mineral oil fromsaid basic temperature to a temperature within 5 F. of its pour point,flowing said oil through a pipeline extending from a shipping point to aterminal point at a temperature within 5 F. of its pour point in atleast a portion of said pipeline, and maintaining the flow rate of saidmineral oil such that the ratio of said flow rate in thousands ofbarrels per day to the square of the inner diameter in inches of saidpipeline is not less than .32 nor more than .42 for said portion of saidpipeline.

5. The method of claim 4 wherein said mineral oil is cooled to atemperature in the range of its pour point to 5 F. above its pour point.

6. The method of claim 4 wherein said mineral oil is cooled to its pourpoint.

7. In a method of transporting a mineral oil having a pour point greaterthan its basic temperature, the steps of heating said mineral oil fromsaid basic temperature to a temperature within 5 F. of its pour point,flowing said mineral oil through a pipeline extending from a shippingpoint to a terminal point at a temperature within 5 F. of its pour pointin at least a portion of said pipeline, and maintaining the flow rate ofsaid oil such that the ratio of said flow rate in thousands of barrelsper day to the square of the inner diameter in inches of said pipelineis not less than .32 nor more than .42 for said portion of saidpipeline.

8. The method of claim 7 wherein said mineral oil is heated to atemperature in the range of its pour point to 5 F. below its pour point.t

9. The method of claim 7 wherein said mineral oil is heated to its pourpoint.

No references cited.

ALAN COHAN, Primary Examiner.

1. IN A METHOD OF TRANSPORTING A MINERAL OIL, THE STEPS OF FLOWING SAIDMINERAL OIL THROUGH A PIPELINE EXTENDING FROM A SHIPPING POINT TO ATERMINAL POINT AT A TEMPERATURE WITHIN 5*F. OF ITS POUR POINT IN ATLEAST A POORTION OF SAID PIPELINE, AND MAINTAINING THE FLOW RATE OF SAIDOIL SUCH THAT THE RATIO OF SAID FLOW RATE IN THOUSANDS OF BAR-